Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of preventing malfunctions caused by aerial discharge.
Description of the Background Art
In a traditional liquid crystal display device, an array substrate with thin film transistors (TFTs) formed thereon and a counter substrate are bonded to each other through a seal along the peripheral portions of these substrates, forming a container for sealing liquid crystals. In general, common wiring (Vcom wiring) is located on the outermost periphery of the array substrate.
The liquid crystal display devices in recent times are required to have a wide viewing angle, so that liquid crystal panels employing the fringe field switching (FFS) mode are commonly used. In the liquid crystal panel employing the FFS mode, both a pixel electrode and a common electrode that control the alignment of the liquid crystals are provided on the array substrate. These two electrodes are laminated via an insulating film therebetween. One of the electrodes that is provided as the upper layer has slits formed therein. A rubbing treatment is performed in the direction that is substantially parallel to the long-side direction of the slits. When the electric potential between the electrodes is the OFF potential, the liquid crystal molecules are aligned in the direction that is substantially parallel to the long sides of the slits. When the electric potential larger than the OFF potential is applied between the electrodes, the electric field (transverse electric field) is generated in the direction that is perpendicular to the long-side direction of the slits, causing the liquid crystal molecules to rotate (in a transverse direction) in the plane that is parallel to the substrate so as to agree with the electric field direction. The amount of transmitted light is regulated by controlling the rotation angle of the liquid crystal molecules. Besides the FFS mode, the in-plane switching (IPS) mode is known as the structure in which both the pixel electrode and the common electrode are provided on the array substrate.
In the liquid crystal display devices in which the FFS mode or the IPS mode is employed, the electrification of the surface of the panel is likely to cause display failures. Thus, a transparent conductive film is formed on the surface of the counter substrate on the side opposite to the liquid crystals and the transparent conductive film is grounded. A grounding method is known which connects GND wiring that is kept at the ground potential of the liquid crystal display device to the transparent conductive film (Japanese Patent Application Laid-Open No. 09-105918 (1997) (for example, FIG. 14).
In recent years, panels including the liquid crystal panels and organic electroluminescent (EL) panels have increasingly reduced size, thickness, and frame width. These panels are equipped with additional functions, such as a touch panel. This is accompanied with increasing number of cases in which static electricity (aerial discharge) from outside the panels (for example, from a human body) causes malfunctions of the panels. Such panels have recently come into use in car navigations and other on-board purposes. Therefore, the strict standard of withstand voltage in the aerial discharge test has been imposed.
According to the aerial discharge tests performed on the liquid crystal panel, static electricity tends to be discharged to the conductive portions of the liquid crystal panel. That is, static electricity is likely to be discharged to the conductive portions of the array substrate and the counter substrate that extend beyond the seal (insulator) and is less likely to be discharged to the portions covered with the seal.
The Vcom wiring is provided along the peripheral portion of the panel on the array-substrate side. A part of the Vcom wiring commonly extends beyond the edge of the seal. Consequently, electric charge generated by electric discharge is transmitted through the Vcom wiring on the array-substrate side and enters a driver integrated circuit (IC) that is chip-on-glass (COG) mounted, is chip-on-film (COF) mounted, or is disposed on a circuit board, possibly causing a malfunction or a breakdown of the driver IC.
As an approach to such a problem, a technique is known by which the Vcom wiring is formed inside of the seal and the GND wiring is formed to surround the outer periphery of the Vcom wiring (Japanese Patent Application Laid-Open No. 2008-46278).
According to Japanese Patent Application Laid-Open No. 2008-46278, a pattern to serve as the GND wiring is located along the outer periphery of the panel. However, patterns of the conductive transparent film located outside of the seal are locally disposed only on the corners of the panel. Such wiring does not have sufficient effect in dissipating static electricity. Moreover, the conductive transparent film, which is formed to be in direct contact with the seal, has a drawback in terms of adhesion. More particularly, while an insulating film composed of, for example, SiN, has an excellent adhesiveness to epoxy resin commonly used as sealing material, a transparent conductive film composed of, for example, indium tin oxide (ITO) that is in direct contact with the seal has insufficient adhesion to the seal, whereby defects such as bubbles and seal punctures are more likely to occur.